Telephone system



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TELEPHONE SYSTEM Filed Nov. 1, 1924 Q SheetS-Sheet 9 I III! III"Patented Oct. 1, 1929 UNITED STATES PATENT OFFICE JOHN E. OSTLINE, OFLIVERPOOL, ENGLAND, ASSIGNOR, BY MESN'E ASSIGNMENTS, TO

AUTOMATIC ELECTRIC INC., OF CHICAGO, I

LLINOIS, A CORPORATION OF DELAWARE TELEPHONE SYSTEM Application filedNovember 1, 1924, Serial No. 747,373, and in. Great Britain November 14,1923.

The present invention concerns improvements in or relating to automaticor semiautomatic telephone systems and more particularly those systemsin which call indicator working is employed, altl'iough a number offeatures of the invention are not limited to these conditions and may beapplied in other circumstances than those immediately concerned withcall indicator Operation.

One of the features of the invention is a special type of impulserepeater which is adapted to repeat the initial series of impulsesreceived by it in one direction only and to repeat subsequent series ofimpulses in another direction only. This feature is of particular valuein connection with call in dicator operation, in which it is oftendesirable that the necessary storage devices should be located at anautomatic exchange and should be arranged to be common to as large agroup of junction lines as possible and not individual to a particularjunction line or to a group of junction lines leading to a particularexchange. Under these circumstances it becomes necessary that theregister devices shall be taken into use prior to the transmission ofthe digit or digits serving for the selection of the particular exchangeto which the call has to be routed and it is clearly unnecessary tostore this digit or digits on the register devices. Hence the necessityarises for the one or more series of impulses which determine thedesired exchange to be repeated to a switch or switches in the speakingroute in order to effect the exchange selection and for subsequentseries of impulses to be then repeated to the registering devices. Anincidental advantage of this arrangei'nent is that it permits amplehunting time for the switch associated with the repeater serving toselect an idle set of registering devices, since this time comprises theduration of a complete train of impulses and the pause at.

either end thereof.

lVhen a repeater is employed such as that described it will be apparentthat the registering devices and the apparatus which may be associatedtherewith for sending out impulses over a trunk line in accordance withthe setting of the registering devices will be used in common for trunklines to various exchanges, which will be in general, of differentlengths. Under these circumstances it becomes advantageous to providecompensating arrangements associated with the impulse sender for varyingthe resistance in the impulse transmitting circuit in accordance withthe characteristics of the inter-exchange trunk line over which theimpulses are to be sent. This modification of the resistance canconveniently be effected by devices similar to those used forregistering the digits of the required number and adapted to be operatedby a digit not forming part of the number to be transmitted over thetrunk line.

Another feature of the invention concerns an improved type of registerset which consists of a single step-by-step switch adapted to respondsuccessively to each of the digits to be recorded and after eachresponse to transfer the digit recorded to one of'a number of groups ofstorage relays. This switch can conveniently be a 25-point rotary lineswitch of known type, arranged to have two normal positions and to movealways in the same direction, and each group of storage relays maycomprise four relays which are energized in various combinations to makethe necessary record.

According to a further feature of the invention a particular arrangementis provided in connection with an impulse sender for sending in thiscase cod-e impulses whereby the speed of the impulse generation may beaccurately determined, and what is of more importance, as a result ofthe inevitable wear of the cont-acts the speed will tend to decreaserather than to increase. Under these circumstances, adjustment mayoriginally be made for the impulse generation to take place at a speedas high as is consistent with the reliable operation of the devicesresponsive thereto; there is then no danger of unreliable operation ofthese devices in course of time, since the speed will tend to decreaserather than to increase. According to this arrangement the rate ofgeneration of impulses is determined by a slow acting relay inconjunction with the controlling magnet of a step-bystep switch, theslow acting relay being adapted to control the operating circuit of saidmagnet and to be short circuited until said magnet is fully energized.For instance, the relay may be normally short circuited by aninterrupter contact on the said magnet, the magnet in turn beingenergized over a back contact of the relay. A further advantageousarrangement contemplated according to the invention is to have amicrometer adjustment for this back contact so that the speed ofimpulses generated may be accurately determined.

Still another feature relates to a special load distributing arrangementwhereby calls are distributed to each operator in turn irrespective ofthe number she has already awaiting attention. This sequence ofoperations is only disturbed if the number of calls awaiting attentionat any particular position reaches a predetermined number or if thecords at that position are in use or if the operator has left theposition.

A further feature relates to an arrangement whereby calls requiringspecial service not ordinarily provided by the regular call indicatoroperator can be routed to a special service operator by the momentarydepression of a single special service key.

Yet another feature of the invention is concerned with an arrangementwhich comes into use momentarily when the transmission of the requirednumber over the trunk line has been completed to test whether thecalling subscriber is still on the line. In case he is not, theconnection is then rel-eased and the number transmitted is not displayedto the manual operator.

These and other features not specifically mentioned at this point willbe better understood from the description of a preferred embodiment ofthe invention which will now be given with reference to the accompanyingdrawings, though it will be understood that this is by way of exampleonly and that various modifications in the circuit details might be madeby those skilled in the art without exceeding the scope of theinvention.

Figure I of the drawings shows a special repeater at the tandemexchange, a coder selecting switch, a selector which responds to thefinal exchange selecting digit, and a secondary line switch at theincoming end of the trunk line. This figure also shows a coder that isto say a device for registering the digits dialled together with a codesending switch for transferring these digits to the distant callindicator position in a particular code.

Figure 2 shows a trunk relay group and a special service trunk finder,and also the necessary switches for determining the sequence in whichcalls shall be dealt with by the de-coder and a special switch for distributing the load equally among the various operators.

Figure 3 shows the call indicator lamps and the decoder, the function ofthe latter being to respond to the code impulses sent over the trunkline and to control the lighting of tie appropriate call indicator lampsso as to display the number to the operator.

Figure l shows a cord circuit and the rotary line switch associatedtherewith together with the meters, supervisory apparatus and operatorsequipment, and also a special service trunk finder and a special.service trunk.

Figure 5 is a diagrammatic representation of the general layout of thesystem from which main principles underlying it may be gathered, whileFigure 6 is a table showing the code into which the Various numericaldigits are converted for sending over the trunk line.

A description will first be given of the general lay-out shown in Fig. 5where it will be assumed that connect-ion is to be extended from thecalling subscriber A to the called subscriber A. Jhen the calling partyA removes his receiver, his individual line switcn C will operate toselect an idle trunk relay group TR with which is then associated anidle register .selector B. Upon receipt of the first digit this will beoperated for instance to the eighth level and will then operate toselect an idle director such as DI. llhe first selector E also respondsto the first series of impulses and then operates to select a selectorsuch as E". he director D1 will thenregister the remainder of the digitsand send out suitable trains of impulses which will in general bedifferent from those sent by the calling subscriber.

The first of these trains will operate a se lector such as the selectorE, the wipers of which will be raised for instance to the eighth leveland will then automatically be rotated in search of a free trunk to arepeater such as R. The repeater R is of special type so arranged thatthe first series of impulses re ceived by it are repeated to asucceeding selector such as D, while subsequent series of impulses arerepeated over the coder selector OS to a coder which comprises all theapparatus enclosed in the dotted rectangle. Ac cordingly when the nextdigit is sent, the selector D will be operated, for instance, to thesixth level and will then select an ille trunk line to the secondaryline switch SL at the required manual exchange.

During the transmission of this digit the coder selector CS will haveselected an idle coder and subsequent digits transmitted will bedirected to the digit recording s itch DES. and will thereupon operatein turn the compensating relay CR and the relays in the storage groupsSS 8G 5G and 8G The purpose of the compensating relays GR is to adjustthe resistance of the trunk line to standard value as will be more fullyunderstood from the detailed description which follows. As soon as allthe digits have been sent the secondar line switch SL is set inoperation to s lect an idle trunk relayset D from among those renderedaccessible by theload distributing switch LDS operating in conjunctionwith the position load distributing relay set LR. At the same time anidle marker S allotted by themarker distributor S is taken into use andthis in conjunction with the set-up control switch S in due courseeffects the connection of the trunk relay group D to the de-coder D thiswill occur when the de-coder has dealt with calls which have come inprior to the one under consideration. lVhen the trunk relay group D isconnected with the de-coder D the sending switch S in the coder isstarted up to send in code over i the trunk line the digits stored onthe storage relay groups SG 8G 8G and SG lVhen this process is completedthe coder is released and reverts to common use and the numbertransmitted over the trunk line in code having been de-code-d at thedecoder is displayed by means of the storage relay groups D on the lampsL at the operators position.

The operator then inserts the plug attached to a cord in the mostconvenient position into the jack of the wanted subscriber, whereuponthe trunk finder TF will bestarted up tofind the trunk relay set whichhas been used.

When this is found, the called subscriber will be rung and when heanswers conversation may proceed in the usual manner. The decoder isreleased as soon as the operator inserts the plug and the set-up controlswitch S is then moved on into association with the next marker whichhas a call waiting to be dealt with. Upon the termination of theconversation the operator will be notified in the usual manner and willwithdraw the plug, whereupon all the operated apparatus will bereleased.

In case the operator sees from the number which has been dialled thatsome special service is required which in the ordinary way it would notbe her business to give, she will press the special service key at herposition, whereupon instead of the trunk finder TF being started up, thespecial service position trunk finder STF is operated to find theparticular trunk relay set in the manner pre viously described. VVhenithas been found the special service trunk finder SST is started up toselect a trunk leading to a jack such as SS at a special serviceoperators position over which the call may be dealt with by the specialoperator. The regular operator need only press the special service keymomentarily and the de-coder is then released and the subsequentconnections are made entirely automatically;

The operation of the system having been described in general'terms, adetailed description will now be given withreference to the circuitdiagrams Figures 1, 2, 3 and 4 which should be placed together with thecorresponding lines in alignment. Portions of the circuits are verysimilar to those disclosed in copending application No. 27,819 of 1923,but there are important differences as will be pointed out. 7

It will be assumed that the repeater in Fig. l is taken into use fromthe bank of an incoming selector such as E. As soon as the selectorswitches through, the following cir-' cuit is completed: battery, upperwinding of relay 4, normally closed springs controlled by armature 45,upper trunkconductor 1, impulsing loop at the director, lower trunkconductor 2, normally closed springs controlled by armature 46, lowerwinding of relay 4 to earth. Relay 4 upon operating, at its armature 5completes a circuit for release relay 7 and at its armature 6 preparesthe impulsing circuit. Relay 7 operates when its circuit is completed,at armature 9 connects earth to release trunk conductor '3, at armature10 completes acircuit for the right hand winding of the shunt fieldrelay 15, at armature 54 prepares a circuit for the series relay 11 andat armature 8 completes a circuit for relay 31 which extends as follows:battery, upper winding of relay 31, back contact and armature 18, frontcontactand armature 8, armature 9 and its front contact, earth. Relay 31thereupon operates and at armature 32 connects earth to the releasetrunkconductor 49, though this operation is without efi'ect at the moment. Acircuit is also completed by relay 7 for starting up the coder selectorswitch as follows: battery, winding of line relay 33, back contact andarmature 40, normally closed springs controlled by armature 23, backcontact and armature 18, front contact and armature 8, armature 9 andits front contact, earth. By operating its armatures 3 4 and 35, relay33 starts the coder selector hunting for an idle coder in known manner.

In response to the transmission of the nextdi it a corres ondin numberof interru tions will be produced in the circuit of line relay 4 and itwill de-energize accordingly. As soon as relay 4 firstpulled up, acircuit was completed over the trunk conductor 48 which circuit extendsas follows: from battery by way of resistance 7 5, back contact andarmature 28, front contact and armature 6, armature and its backcontact, back contact and armature 24 t0 conductor 48, and through thelower winding of the line relay (not shown) of the selector D to ground.Consequently each time relay 4 deenergizes, this bridge is opened atarmature 6 and the succeeding selector D, indicated by the dottedrectangle, is-

operated accordingly. Upon the first deen ergization of relay 4, acircuit is completed over armatures 10 and 13 for series relay 11 whichenergizes and being slow to release, remains energized throughout theseries of im pulses. Relay 11 upon operating, at its armature 12 opensanother point in the connection between release trunk conductor 3 andrelease trunk conductor 49 and at its armature 13 completes a circuitfor the lower winding of relay 25. This relay is of the two-step typeand in response to current flowing through its lower winding operatesits lightly adjusted armature 27 whereupon earth is connected to bothends of its upper winding.

When the first series of impulses ceases, the selector D will hunt inknown manner to find an idle trunk line to the required manual exchange,and having found one, will switch through. After having switchedthrough, the selector D is held up by earth on release trunk conductor49 by way of armature 32. The conductors 47 and 48 are now extended tothe conductors 200 and 201 leading to the position selector havingwipers 230, 210 and 231. The position selector is not operated at thistime, however,notwithstanding the battery connection thru resistance toconductor 48, as conductor 47 over which the line relay 206 must beoperated is free from operating potential at this time.

On the termination of the series of impulses and after a sufiicient timehas lapsed to permit the selector D to complete the above mentionedtrunk hunting operation and switch through, relay 11 deenergizes andearth is then removed from the middle point of the winding of relay 25which accordingly oper ates fully, and at its armature 26 opens a pointin its original energizing circuit, at armatures 28 and 30 opens thebridge across conductors 47 and 48 and at armature 29 and the frontcontact of armature 30 prepares a new impulsing circuit so thatsucceeding trains of impulses are sent to the coder, while at the frontcontact of armature 28 a circuit is prepared for relay 20.

In the meantime, the coder selector will have been hunting to find anidle coder, and when test wiper 53 engages a contact which is notearthed, switching relay 38 is not longer short circuited and energizesin series with rotary magnet 36 which is however not now operated.Thereupon wipers 50 and 51 are connected through to the outgoing trunkconductors at armatures 39 and 43, at armature 40 relay 33 isdisconnected and at the front contact of this armature and the frontcontact of armature 41 earth fromarrnature 9 is connected to the testwiper 53, while at the front contact of armature 42 the impulsingcircuit is prepared.

Upon the transmission of the next digit, the following circuit iscompleted on each deenergization of relay 4: battery, winding of magnetof the digit recording switch, winding of series relay 65, back contactand armature 74, lead 62, wiper 52, front contact and armature 42, frontcontact and armature 30, armature 6 and its back contact, armature 29and its front contact, armature 10 and its front contact to earth. Thedigit recording switch is thus advanced by the operation of its drivingmagnet a number of steps corresponding to the value of the digitdialled. Relay 65 is energized in series with the magnet and at itsarmature 65 completes a circuit forrelay 67. This relay thereupon at itsarmature 68 prepares a circuit'for operating the storage relays and atarmature 69 prepares a circuit for the relay 98.

At this point it may be desirable to eX- plain the purpose and operationof relays 92 and" 93. It Will be clear from what has already been saidthat access may be had from the repeater in Fig. 1 to any one of anumber of exchanges as determined by the setting of the selector D.Furthermore the length of the trunk lines leading to the differentexchanges may vary considerably and as the coder at the distantexchangecontains relays which are marginally operated by currents overthe trunk line, it will be apparent that some difiiculty or at leastinconvenience may be caused by the fact that these relays in the variousdecoders at the same exchange in order to operate reliably will have tobe differently adjusted so as to respond correctly to codes transmittedfrom a number of other exchanges. In order to overcome this diflicultyand to permit a standard adjustment of the relays in question, thecompensating relays 92 and 93 have been introduced at the de-coder. Theoperation of these relays is controlled by sending an extra digitimmediately preceding those which are to operate the storage relays inthe coder and are subsequently to be displayed at the call indicatorposition. This is particularly easy to achieve if, as in the arrangementnow being described, the digits dialled by a subscriber are received bya register translator or director from which impulses are sent out whichwill in general be difierent from those received by the director. Thesending of an extra train of impulses in this case can be effected bymaking an additional cross connection to the impulse sender. The digitfor effecting the compensation will preferably be either 1, 2, 3 or 4and in response theretp either one or both or neither of the relays 92and 93 will be operated. The contacts 94 and 96 controlled by them arearranged to short circuit the resistances 104 and 105 respectively,which are connected in the circuit over which the code impulses aresent.

Let it be assumed in the present instance, that the digit sent forcompensating purposes is 3 and that the wanted subscribers numbersubsequently recorded in the coder is 4567. in response to thecompensating digit 3 therefore the wipers 82, 83, 84 and 85 of the digitrecording switch will be moved three steps, so that the wiper 82 comesinto engagement with contact 106, while wiper 84 comes into engagementwith contact 107. At the end of the series of impulses, relaydecnergizes and a circuit is then momentarily completed from earth,armature 66 and its back contact, armature 68 and its front contact,wiper 82, contact. 106, lead 89, armature 99 and its back contact.winding of relay 93 to battery, and parallel thereto over wiper 83,contact 107, lead 90, armature 100 and its back contact, winding ofrelay 92 to battery. Relays 92 and 93 upon operating, at armatures 95and 97 lock themselves up to the holding earth in the repeater by way ofarmature 73 and its back contact, and lead 63, and at armatures 94 and96 remove the shunts around resistances 104 and 105, respectively, sothat both these resistances are included in the code sending circuitover the trunk conductors: this case will clearly cor respond to a shorttrunk line to a nearby exchange. A circuit is also completed on thedeenergization of relay 65 from earth at armature 66, armature 69 andits front contact, armature 103 and its back contact, up per winding ofrelay 98 to battery. Relay 98 is also of the two-step type similar torelay 25 and thereupon operates its light contact 102. Upon thedeenergization of relay 67, earth is removedfrom the middle point of thewinding of relay 98 and it then operates fully; at its armature 103transfers its original energizing circuit to relay 108 and at armatures99, 100 and 101 connects the leads from the various bank contacts of thedigit recording switch througl'i to the relays of the first storagegroup. When armature 69 engages with its back contact a circuit iscompleted over the niultipled contacts in the bank of wiper 85 and saidwiper and interrupter contact 81 for automatically restoring the digitrecording switch to normal. This switch will from the nature of thingsnever have to take more than 10 steps to respond to a particular digitand as it is convenient to use for this purpose an ordinary rotary lineswitch moving always in the same direction, which switch has 25confacts, it will probably be desirable to multiple the contacts of thebank together in two halves so that the switch will have two normalpositions. In this case therefore the switch will come to rest withwiper 85 rest ing on the dead contact 86.

The digit 4 will now be sent out from the director, in accordance withwhich the wipers of the digit recording switch will be advanced foursteps. When relay 65 deenergizes, a circuit will be completed fromearth,

armature 66 and its back contact, armature 68 and its front contact,wiper 82, contact 109, lead 88, armature 101 and its front contact,armature 110 and its back contact for relay 111. Relay 111 at armature112 completes a locking circuit for. itself to the earth on the repeaterand at armature 113 prepares a circuit for sending the appropriate code119, 110 and 120 transfers the connections of loads 88, 89, 90 and 91 tothe second storage I relay group. I

The next digit on the assumption made above is 5; consequently upon thereceipt of this digit the wipers 82, 83, 84 and 85 are stepped aroundinto their fifth position. then relay 65 releases, a circuit iscompleted over wiper 84 for relay 121 which operates to prepare the codesending circuit at armature, 122 and at armature 123 locks itself up.

Relay 117 is similar to relays 108 and 98 and is partially energizedwhen relay 65 releases and is fully energized when relay 67 releases andthereby transfers the operating circuits to the third storage group.

then the next digit 6 is sent, the digit recording switch takes sixsteps, whereupon on the deenergization of relay 65 circuits. arecompleted over wipers 82 and 84 for relays 125 and 126 which look up andprepare code sending circuits in the manner previously described. Relay124 is operated fully when armature 69 leaves its front contact andtransfers the operating leads to the fourth storage group and theconnection over lead 116 to relay 127.

The transmission of the last digit 7 results in the operation of relays128 and 129 which look up and prepare code sending circuits in the samemanner as the other storage relays.

relay 127 operates its light contact 130 when earth is first connectedto the middle point,

of its winding over lead 116 and when this earth is removed operatesfully. At armatures 131,132, 133 and 134 the circuits for the fourth setof storage relays are opened so as to preventany accidental furtheroperation, at armature 135 relay127 opens its own initial energizingcircuit, at armature 136 it opens the initial energizing circuit ofrelay 7 5, at armature 137 prepares a holding earth connection to lead63 'andat'armature 138 prepares a circuit over lead 139 for starting thesending of code impulses. Relay 7 5 was energized over armature 136 andits back contact at the same time as relay 127 was partially energizedand at armature 78 opened the code impulse starting circuit, and atarmature 76 removed earth from armature 137. Relay also by operating itsarmatures 77 and 79 connected itself over its upper winding in a lockingcircuit which extends as follows: battery, winding of line relay 206, ofthe incoming secondary line switch, back contact and armature 203, uppertrunk conductor 200, through the selector D, conductor 47, armature 21and its back contact, armature 39 and its front contact, Wiper 50, lead60, armature 79 and its front contact, upper winding of relay 75, frontcontact and armature 66, lead 61, wiper 51, front contact and armature43, back contact and armature 24, conductor 48, through the selector D,conductor 201, armature 204 and its back contact, earth.

Relay 206 is energized in this circuit and by operating its armatures207 and 208 starts the incoming rotary line switch hunting for a freetrunk .over which the connection may be completed. This huntingoperation takes place in known manner and as soon as an idle trunk isfound, relay 202 being no longer short circuited, energizes in serieswith magnet 209 and at its armatures 203 and 204 disconnects relay 206and connects the trunk leads through, while at armature 205 it completesa locking circuit for itself. Relay 7 5 is not deenergized by themomentary opening of its circuit consequent on the operation of itsarmatures 203 and 204, and when this has taken place, the circuit formaintaining it energized extends as follows: from battery, upper windingof relay 212 back contact and armature 225, back contact and armature224, back contact and armature 223, the trunk conductor 220, wiper 230,front contact and armature 203, conductor 200, thence over thepreviously traced circuit to conductor 201, armature 204 and its frontcontact, wiper 231, conductor 221, armature 226 and its back contact,armature 227 and its back contact, armature 228 and its back contact,armature 229 and its back contact, earth.

Before proceeding further with the description of the actual operationof setting up a call, it will be desirable to explain the circumstancesunder which a trunk such as that shown in Figure 2 is renderedaccessible to an incoming secondary line switch. In order to ensure thatcalls shall be distributed equally among the operators so that no oneoperator receives more or less than her fair share, a set of positionload distributing relays is provided for each position and these operatein conjunction with a load distributing switch which is common to agroup of positions. The effect of these arrangements is that for eachcall that comes in a definite operators position is preselected so thatthe calls are distributed to each operator in turn until they have eachreceived one, the subsequent distribution being continued in the samemanner irrespective of whether the first call has been dealt with ornot. Arrangements are also provided to prevent more than a certainnumber, in this case five, calls accumulating at any operators positionand should this condition of aifairs arise, an alarm is given to asupervisor to indicate that the position is .overloaded. A position isalso rendered inaccessible if the operator leaves it or if all her cordsare in use as will be more fully explained hereafter.

Suppose in the present instance that the position at which the trunkshown is located has two calls awaiting attention and that the wipers242 and 243 of the load distributing switch have just arrived again onthe contacts 244 and 245 associated with this position. In thesecircumstances relay 234 will be energized in the following circuit:earth, armature 241 and its back contact, wiper 242, contact 243,winding of relay 234 to battery. The operation of relay 234 which thentakes place closes contact 237 whereby a locking circuit is prepared forrelay 233 and contact 238 whereby an energizing circuit is prepared forrelay 233 and earth is removed from the position busy common lead 232 soas to render the idle trunks in this position selectable. vVhen theswitching relay 202 of the incoming rotary line switch switches througha circuit is momentarily completed as follows: earth, front contact andarmature 207, front contact and armature 205, wiper 210, release trunkconductor 222, normally closed springs controlled by armature 218,common lead 232, armature 235 and its front contact, winding of relay233 to battery. Relay 233 accordingly operates, at armature 235completes the previously prepared locking circuit for itself and atarmature 236 completes a circuit extending from earth, front contact andarmature 235, contact 245, wiper 243, relay 239 to battery. Relay 239upon operating, at armature 241 opens the circuit of relay 234 and atthe front contact of this armature completes a circuit for the drivingmagnet 240 so that the distributing switch takes one step. Relays 233and 234 are thus deenergized and earth is replaced on the common lead232. It is then impossible for any further calls to come to the positionin question until a call has been received by each of the otherpositions unless they are inaccessible for any of the reasons mentionedabove. In such a case, earth would be connected to the leadcorresponding to lead 246 and relay 239 would be again energized overthe back contact of the armature corresponding to armature 236. Thedistributing switch therefore takes a further step and no call isreceived at that particular position.

To return now to the consideration of the operations taking place in thetrunk relay set, relay 212 energizes in series with relay when the lineswitch switches through. Thereupon at its armature 213 it completes acircuit for relay 217, at armature 214 prepares a locking circuit foritself, at armature 215 prepares a circuit for relay 247. and removesearth from contact 302 in'the bank of wiper 300 and at armature 216connects earth over the common lead 316 to the wiper 317 of the markerdistributor.

It should be explained that in order to ensure that calls arriving at aposition are dealt with in the proper order, a number of markers areprovided, in the case considered five, this representing the maximumnumber of uncompleted calls that it .is desirable should existsimultaneously at any one position. These markers have two banks whichare connected. to the various trunk relay sets in the position. Theorder in which the markers are taken into use is controlled by a markerdistributor, of which only one is provided per position and it isfurther necessary to have a set up control switch, the function of whichis to connect up the decoder in turn to various trunks which have beentaken into use so that the number may be sent in the special code fromthe recording devices at the tandem exchange, so as to operate theproper lamp and indicate to the operator the wanted numher. Thenecessity for the set up control switch as well as the markerdistributor is on account of the difference in the rate at which callsarrive at the position and the rate at which the operator deals withthem. Thus if four calls come to a position almost simultaneously themarker distributor will operate to assign four markers in quicksuccession; the set-upcontrol switch, however, will lag somewhat andwill move on to permit the display of the fourth call after the otherthree have been displayed and dealt with.

Let it be assumed that when the call arrives the marker distributor isin the position shown, the marker shown is in any'other position and theset up control switch wipers are resting on the contacts next beforethose with which they are shown in engagement. Accordingly when relay212 operates a circuit will be completed as follows: earth, armature 252and its back contact, front contact and armature 216, common lead 316,wiper 317 of the marker distributor, contact 318 associated with themarker shown on which it is resting, armature 311 and its back contact,winding of relay 312 to battery. Relay 312 is thereupon energized and byoperating its armatures 313 and 314 starts the selected marker huntingfor the contact 302 in the bank wiper 300, from which earth has beenremoved by the operation of armature 215. hen this contact is found,relay 305 is no longer short circuited and energizes, thereby at contact311 opening the circuit of relay 312 and at contact 310 completing alocking circuit for itself. Furthermore at armature 309 a circuit iscompleted for the driving magnet 324 of the marker distributor whichthereupon operates so as to allot another marker and at armature 308 acircuit is completed for relay 327 in the setup control switch. Relay305 also at armature 306 removes one earth connection from lead 337 ofthe chain busyingcircuit and at the front contact of this armaturelights the marker pilot lamp 469 at the operators position so as toindicate which marker is in use, at the same time by operating relay 470lighting lamp 47 2 to show that a call is awaiting attention.

following circuit is completed: earth, front i contact and armature 313,front contact and armature 31.0, wiper 300, armature 302, armature 215and its front contact, lower winding of relay 247 to battery. Relay 247thereupon operates, at its armature 245 prepares a circuit for relay259, at armature 249 prepares a locking circuit for relay 260, atarmature 250 prepares a locking circuit for itself through its own upperwinding, at armature 251 completes a locking circuit through its ownlower winding which circuit also serves to maintain relay 305 energized,at armature 252' removes earth from the marker start common lead 316 andat armature 253 prepares a locking circuit for relay 254.

The operation of the set-up control switch must now be considered. readymentioned, it is assumed that wiper 325 is standing on the contactimmediately before contact 326 and that the de-coder is connected to thetrunk corresponding to this contact. Under these circumstances, relay327 will be energized by earth over the armature similar to 308 of themarker in use for the other connection and relay 330 will also beenergized. This state of affairs Wlll continue until the call has beencompletely decoded, whereupon in a circuit which will be tracedsubsequently, the

earth connected to the contact upon which wiper 325 is standing 1Sremoved momentarily and is then replaced over the bank contact of thearmature corresponding to 307 in the other marker. When this occurs,relay 230 deenergizes, but owing to the operation of armature 308, relay327 will remain energized and a circuit will consequently be againcompleted over armatures 328 and 331 for relay 334. This relay, byoperating its armatures 335, and 336, starts the set-up control As hasbeen al-.

switch hunting. In the case under consideration it will only have totake one step and it will then encounter the contact 326 from whichearth has been removed by the operation of armature 307. Relay 330thereupon energizing, at armature 331 opens the circuit of relay 334 andat armature 332 completes the following circuit, earth, front contactand armature 335, front contact and armature 352, front contact andarmature 329, wiper 325, contact 326, armature 307 and its frontcontact, wiper 301, contact 303, winding of relay 254, armature 214 andits front contact, lower winding of relay 212 to battery. The circuitthus completed serves to maintain the relay 212 energized when its upperwinding is disconnected on the operation of relay 254. Relay 254 at itsarmatures 224 and 227 connects the trunk leads 220 and 221 through byway of the leads 27 6 and 277 to the code re ceiving relays 501, 502 and503, at armature 255 prepares a testing circuit for a purpose which willbe explained subsequently, at armature 256 completes a locking circuitfor itself which also serves to maintain relay 330 energized after relay334 releases, at armature 267 completes a circuit for relay 500 and atarmature 258 prepares a circuit through the lower winding of relay 260.

In consequence of the operation of relay 254 the feeding current isdisconnected from the winding of relay at the coder and in consequencethereof it deenergizes after a short interval. A. circuit for startingthe sending of the code impulses is then completed as follows earth,armature 76 and its back contact, armature 137 and its front contact,back contact and armature 73, armature 138 and its front contact,armature 7 8 and its back contact, lead 139, first contact in the bankof wiper 142 and said wiper, lead 146, armature 71 and its back contact,lead 147, winding of magnet 143 to battery.

It will be as well to describe at this point the inter-operation ofmagnet 143, its interrupter contact 144 and the relay 70. Relay 7 0 isarranged to be normally short circuited by the interrupter contact 144over leads 145 and 146 but when the contact 144 is opened on theoperation of the magnet it is enabled to energize and thus opens its owncontact 71, whereby the circuit of the magnet 143 is opened and itreleases. The contact 71 is provided with a micrometer adjustment, theoperation of which serves to determine accurately the rate of generationof impulses. This adjustment is normally set to effect the generation ofimpulses at a rate which is as high as possible consistent with thereliable operation of the devices controlled thereby and in case anywear should occur, the efi'ect will be to make the generation ofimpulses take place at a. somewhat slower rather than a quicker rate;consequently there is no danger of faulty operation due to impulsesbeing sent .too quickly when any such wear has taken place after thelapse of time. If and when the reduction in speed becomes appreciable itis a comparatively simple matter to re-set the contact 71 of the relay70 by means of the micrometer adjustment so that the impulses will againbe generated at the maximum permissible rate.

Returning now to the operation in this par ticular case, the codesending switch thus commences to rotate its wipers when the abovecircuit is completed. On the first step wiper 142 finds earth over itssecond contact, all the contacts in the bank of wiper 142 being multiplyconnected to earth with the exception of two, one corresponding to thenormal position of the switch which is connected to lead 139 and thetwenty third contact 148 which is connected to lead 149 and controls therelease of the coder in a manner which will be described fullyhereafter. The effect of these multipled contacts is that as soon as theswitch is stepped off normal, it continues to step round under the jointcontrol of interrupter contact 144 and the contact 71 of relay 7 0 untilit again reaches normal position. Wipers 140 and 141 of the code sendingswitch are connected respectively to the lead 60 and 61 and thence overthe trunk line to the relays 501, 502 and 503 in the decoder. The banksof these wipers are so connected up that for each digit which it isdesired to send incode the switch takes four steps.

The impulses sent over the trunk line are of three kinds which may betermed positive, light negative and heavy negative, and of the relayswhich respond to them, relay 501 is polarized in such a manner as torespond to what is termed a positive impulse, relay 503 is polarized inthe opposite direction so as to respond to a negative impulse whilerelay 502 is marginally adjusted and will only respond when a strongercurrent is sent over the line, this corresponding to what has beentermed a heavy negative impulse since no heavy positive impulses areemployed. It is also ar ranged for reasons which will appearsubsequently that a negative impulse, either of the'light or heavyvariety is always sent out on the second and fourth of the four steps ofthe sender switch, while a positive impulse may be transmitted only onthe first and third steps. The combinations of these impulses which areused to characterize the various digits are shown in the table in Fig. 6which also indicates which relays (assumed numbered from right to left)of a storage group must be operated in order that these particularimpulses shall be generated.

In the present case it will be remembered that the number received bythe coder was 34567, of which the first digit 3 was only employed fordetermining which compensating resistance, if any, should be included inthe circuit: consequently it is clearly unnecessary and undesirable thatthis should be transmitted to the decoder. The relays 92 and 93therefore, operated by the compensating digit have no contacts havingdirect connection with the banks of wipers 140 and 141.

Since in accordance with the digit 4, only relay 111 of the firststorage group is operated, when the code sending switch arrives at theposition for sending the first impulse for the first digit, that is tosay, after taking two steps from its normal position, no circuit will becompleted; consequently no effect is produced at this time.

On the next step, however, an impulse, is sent over the followingcircuit: battery, resistance 105, resistance 104, high resistance 151,back contact and armature 154, contact 150, wiper 140, lead 60, wiper50, front contact and armature 39, back contact and armature 21,conductor 47, conductor 200, armature 203 and its front contact, wiper230, conductor 220, armature 223 and its back contact, armature 224 andits front contact, lead 276, relay 501, relay 502, relay 503, lead 277,front contact and armature 227, back contact and armature 226, conductor221, wiper 231, front contact and armature 204, lead 201, lead 49,armature 24 and its back contact, armature 42 and its front contact,wiper 51, lead 61, wiper 141, contact 153 to earth. Current in thisdirection constitutes what is understood as a negative impulse and asthe high resistance 151 has been included in the circuit rather than thelow resistance 152 it will be a light negative impulse and consequentlyonly relay 503 will be operated. A circuit is there upon completed asfollows: earth, armature 506 and its front contact, armature 505 and itsfront contact, armature 516 and its back contact, lower winding of relay509 to battery. Relays 508 and 509 are each of the two-step type havinga light contact which alone is operated when the relay is energizedthrough one winding only: consequently armature 513 is now operated. Onthe termination of this impulse, when the code sending switch steps onto the next contact and relay 503 is deenergized, relay 509 pulls upcompletely, at armature 512 prepares a locking circuit for relay 508, atarmatures 514 and 515 alters the connections to the first set-up relaygroup, and at armature 516 opens its own initial energizing circuit andprepares circuits for the lower windings of relays 508 and 517.

lVhen the code sending switch advances to its next position, a circuitis completed in consequence of the operation of relay 111 as follows:battery, resistance 105, resistance 104, high resistance 151, frontcontact and armature 113, fourth contact in the bank of wiper 141 andsaid wiper, lead 61, wiper 51, front contact and armature 43, backcontact and armature 24, conductor 48, conductor 201., armature 204 andits front contact, wipcisely or 231, conductor 221, armature 226 and its21 and its back contact, armature 39 and its.

front contact, wiper 50, lead 60, wiper 140, fourth cont-act in itsbank, earth. It will be noticed that the direction of current flow inthis circuit is opposite to that in the circuit previously traced andthat this current accordingly constitutes a positive impulse. The effectof this positive impulse is to operate only relay 501 which completes acircuit as follows: earth, armature 506 and its front contact, armature507 and its front contact, armature 514 and its front contact, armature523 and its back contact, relay 524 to battery. Relay 524 thereuponoperates, at its armature 525 looks itself up by way of lead 526 to theearth on armature 506 and at its armature 527 prepares a circuit of theupper winding of relay 528.

The code sending switch will now take another step whereupon a lightnegative impulse will be transmitted over a circuit presimilar to thatpreviously traced for such an impulse; the effects at the decoder arehowever slightly different in this case,

owing to the operation of relay 509. As soon as relay 503 picks up, acircuit is completed for the lower winding of relays 508 and 517 whichthereupon operate their light contacts 511 and 518, respectively,thereby short circuiting their upper windings. On the ter- -1ni11ationof'the impulse when armature 505 leaves its front contact, both theserelays energize fully over their two windings in series. Relay 508 atits armature 510 opens the locking circuit of relay 509, which thereupondeenergizes and at armature 512 opens the locking circuit of relay 508so that both these relays are thus deenergized. Relay 517 operates itscontacts 519, 520, 521, 522 and 523 whereupon its own energizing circuitis transferred to a similar relay of the set cor responding to thesecond digit and the operating circuits are transferred to the secondset-up relay group. The setup and storage relays corresponding to thesecond and third digits are not shown since they are similar in allrespects to those for the first digit; their position is indicated bythe dotted rectangles.

The next digit to be transmitted in code is 5 and reference to the tablein Fig. 6 will show that this is done by sending a light negativeimpulse followed by a heavy negative impulse. The effect of the initiallight negative impulse is similar to that described previously, namely,that relay 509 is energized and locked up but that none of the set-uprelays is energized,

Upon the receipt of the following heavy negative impulse, relay 502 isoperated as well as relay 503 whereby a circuit is completed overarmature 504 and its front contact, armature 515 and its front contact,armature 521 and its front contact for the fourth relay in the secondset-up group which thereupon locks up to lead 526 and prepares a circuitfor the corresponding relay in the storage group. This impulse also hasthe effect of energizing relay 508 and the changeover relaycorresponding to 517 after which both relays 508 and 509 deenergize, andthe circuit is left in readiness for the receipt of the next digit.

The digit 6 now to be transmitted involves the sending of a positiveimpulse in'the first position of the code sending switch for this digit,that is to say, with the wipers resting on the eleventh contacts. Acircuit substantially identical with that over which this impulse issent has been traced in connection with the sending of the digit 4 andit need not be repeated. The effect of the de-coder is to energize thefirst relay in the third set-up group which thereupon locks up and propares the circuit for the corresponding storage relay as before.The'light negative impulse which is then sent merely serves to operatethe relay 509. In the next position of the sending switch no impulse issent at all and in the following position a heavy negative impulse whichas previously described operates the fourth relay of the set-up groupand restores relays 508 and 509 to normal.

The final digit 7 is sent by means of two negative impulses, the firstof which effects the operation of the second relay 530 in the fourthset-up group. This relay locks itself up at its upper armature and atits lower armature prepares spending storage relay. Relay 509 is alsoenergized and locked up by this impulse in well knownmanner. Thesucceeding heavy negative impulse effects the completion of a circuitfor the fourth set-up relay 533 which operates in a similar manner tothe others. Relays 508 and 509 restore to normal in the usual manner andupon the termination of the impulse relay 531 is energized. Thisoperates armatures 529, 532, 534 and 535 whereby the fourth digit relayset is disconnected so as to prevent any subsequent accidentaloperation; at armature 536 opens the circuit of relay 542 which haspreviously been energized though in this case without useful function,at armature 537 prepares a circuit for energizing the storage relays andat armature 538 prepares a circuit for relay 543.

For the sake of convenience of description it will be assumed that whenthe decoder is taken into use for the call under consideration theoperator has already dealt with the previous call and consequently thereis no number displayed on the call indicator lamps.

a circuit for its corre- This assumption is not altogether consistentwith the previous assumption employed for explaining the operation ofthe set-up control switch but this is immaterial as regards the properworking of the apparatus and simplifies the description of thesubsequent operations. l/Vith this assumption therefore, a short whileafter the energization of relay 531, after relay 542 has deenergizedowing to its circuit being opened at armature 536, the following circuitis completed: earth, armature 544 and its back contact, armature 547 andits back contact, armature 537 and its front contact, armature 549 andits back contact, lead 552 to battery through the up per windings of thestorage relays whose circuits have been previously prepared by theoperation of their corresponding set-up relays. The storage relaysthereupon operate and lock up to lead 553 to which earth is connectedover armature 506 and its front contact, normally closed springscontrolled by armature 546 and armature 548 and its back contact.

The earth connection to lead 552 also extends over armature 258 and itsfront contact through the lower winding of relay 260 to battery so thatthis relay is operated. At armature 261 it closes another point in thecircuit of relay 259, at armature 263 prepares a circuit for relay 266,at armature 264 removes earth from test contacts 27 3 and 274, atarmature 265 opens the locking circuits of relays 212 and 251 and atarmature 229 removes earth from the lower trunlr conductor andsubstitutes battery for a purpose which will be described subsequently.Relay 260 also at its armature 262 completes the following lockingcircuit for itself; earth, back contact and armature 268, upper windingof relay 260, front contact and armature 262, back contact and armature270, front contact and armature 249, lead 272, lower winding of relay539 to battery. Upon the release of relays 212 and 254, the trunk relayset is disconnected from the common leads to the decoder, and earth isremoved from the contacts engaged by wiper 300 of the marker and wiper325 of the set-up control switch. In consequence, relay 305 isdeenergized and the marker is rendered available for use in setting upanother connection and the set-up control switch steps on as previouslyexplained and controls the association of the de-coder with anothertrunk relay group.

Relay 539 operates when its circuit is completed, at armature 545completes a circuit for relay 540, at the same time opening the initialenergizing circuit of the storage relays, at armature 545 completes thedisplay circuit whereby the required number is displayed to the operatorby the lighting of the appropriate call indicator lamps and at armature546 connects a further earth to lead 553 to replace that which isremoved by the deenergization of relay 500 when its circuit is opened atarmature 257. Since relay 539 energizes before relay 500 'deenergizesthis latter operation is effected without discontinuity and the storagerelays remain operated. The deenergization of relay 500, however,removes earth from lead 526 whereby the operated setup relays aredeenergized and also the change over relays such as 517 and 531. Theoperation of relay 540 which takes place at this time opens anotherpoint in the connection to lead 552 and prepares a circuit for relay541.

The condition of affairs so that only relays 217, 247 and 260 in thetrunk relay group are energized and the marker and set-up control switchhave been released as well as the de-coder proper. Only relays 539 and540 remain energized and the storage relays which are effecting thedisplay of the number to the operator. These conditions persist untilthe operator deals with the call.

Consider now therefore thestate of affairs at the coder upon thecompletion of the sending of the code impulses. The code sending switchcontinues to operate in the manner described until it has made'acomplete revolution, i. e., until wiper 142 arrives once more on thecontact connected to lead 139 which is .not now earthed. When it reachesits twenty-third contact, however, wiper 142 finds earth through the lowresistance relay 72 instead of direct and relay 72 is thereby energized.At its armature 73 it removes the locking earth from all the operatedstorage relays in the coder and also the change over relays 98, 117,124, and 127 and these accordingly deenergize. Moreover at its armature74 it completes the following circuit: from earth front contact andarmature 74, lead 62, wiper 52, front contact and armature 42, frontcontact and armature 31, armature 6 and its front contact, armature 28and its front contact, winding of relay 20 to battery. Relay 20 uponoperating, at armatures 21 and 24 switches the speaking leads through atarmat-ure 22 opens the circuit of the busy relay 17 and at armature 23completes a locking circuit for itself at the same time releasing thecoder selector and the coder which then reverts to common use. Theswitching through of the speaking leads has no particular effect at themoment.

Returning now to the further progress of the call, the operator, uponnoting the number displayed on the call indicator lamps, will take up aplug associated with a convenient idle cord circuit and will test thejack of the wanted subscriber by touching the tip of the plug againstthe ring of the jack. If the called line is busy a circuit will becompleted as follows: battery through the winding of the sleeve relaysuch as 411 associated with another operators cord, ring of jack, tip ofplug, normally closed contacts controlled by armature 412, lead 413,winding 414 of the induction coil to earth; this circuit willconsequently induce a click in the operators head set over the plug 415.

It will be assumed, however, in the present case that the wanted numberis idle when called and consequently the operator will insort the plugfully into the subscribers jack,

whereupon a circuit 1s completed from battery, winding of relay 411,ring of plug, sleeve of jack, subscribers cut-off relay toearth. Thesleeve and cut-off relays operate in series and the latter clears thesubscribers line of'its normal battery and earth connections in theusual manner. Relay 411 upon operating, at armature 412 disconnects theoperators head set and completes the upper speaking lead, at armature418 lights the supervisory lamp 419 and at armature417 completes acircuit for the rotary, line switch associated with the cord as follows:earth, armature 417 and its front contact, normally closed springscontrolled by armature 420, armature 421 and its back contact, windingof relay 404 to battery. Relay 404 thereupon energizes and starts theline switch hunting in the usual manner for the contact 274 associatedwith the trunk over which the call is to be completed from which earthwas removed by the operation of relay 250. When the marked trunk isfound, relay 405 is operated whereby the speaking leads 7 from thecalling subscriber are switched through, relay 404 is disconnected andearth is connected over wiper 403 to the test contact associated withthe trunk line in use. A circuit is thereupon completed for relay 266which operates and at armatures 223 and 228 cuts off the batteryconnections from the trunk line, at armature 267 places a further earthconnection on release trunk 222 and at armature 269 completes a lockingcircuit for itself.

Furthermore at armature 269, relay 266 breaks the circuit of relays 260and 539 so that both these relays deenergize, the former at armature 265opening the circuit of relay 247 which also deenergizes. Upon thedeenergization of relay 539 a circuit is completed for relay 541 whichat its armature 548 opens the locking circuit of the storage relays sothat they deenergized. Furthermore, at armature 545 the circuit for thelamps is broken so that the number displayed is extinguished. All

the apparatus associated with the decoder is thus released.

It may happen, however, if the operator is working at high speed thatanother call will have come to the decoder while she was completing thefirst. In this case all the appropriate set-up relays will have beenoperated and further operations will be awaiting the earthing of lead552. This occurs when relay 540 deenergizes whereupon the storage relaysare again operated in accordance with the new

